With a decrease in the size and the thickness of electronic devices, a surface-mounted package is often used as electronic components provided in the electronic device. A specific example of such an electronic component package includes a semiconductor package in which an electronic component such as a semiconductor element is mounted on a surface of a substrate such as a board-on-chip (BOC) and the electronic component is sealed by a resin.
In general, for a copper-clad laminate for semiconductor packages, a reduced warpage is required in a substrate (copper-clad laminate) because an IC chip is mounted thereon. However, in particular, in a sealing step after an IC chip is mounted on an electronic circuit substrate obtained by processing the copper-clad laminate, since the substrate is bonded to a sealing material having a relatively large thermal shrinkage, a deformation such as a warpage may occur due to a difference in the coefficient of thermal expansion (CTE) between the sealing resin and the substrate. This warpage may cause a problem such as a line clogging in a subsequent reflow step or a misalignment of the cutting positions in a cutting step where the substrate is cut to a product size.
In order to suppress such a warpage (curl), conventionally, the use of a laminate formed by laminating a plurality of semi-cured prepregs obtained by impregnating a thin glass cloth with a resin varnish and drying the same and heating and pressing the prepregs is known.
More specifically, for example, Patent Document 1 discloses a method of manufacturing a metal foil-clad laminate, including impregnating a sheet-like base material with a heat-curable resin and drying the same to obtain a prepreg, placing a metal foil on a surface of the prepreg layer, and heating and pressing the prepreg layer to form the metal foil-clad laminate, the method including: applying a first resin composition including an acrylic rubber, an epoxy resin, a phenol resin, and an inorganic filler to a roughened surface of the metal foil; applying a second resin composition of which the adhesive property disappears in a dried state and of which the elastic modulus is higher than the first resin composition to the application surface and drying the same; and superimposing the application surface on the prepreg layer and performing the heating and pressing to form a low elastic resin layer formed from a first resin composition having a thickness of at least 20 μm and an elastic modulus of not more than 10 kgf/mm2 immediately below the metal foil.
According to Patent Document 1, it is disclosed that the metal foil-clad laminate obtained by laminating a plurality of prepregs and pressing the same is ideally used as a surface-mounted printed wiring board material and that solder connection reliability of surface-mounted low-thermal expansion components can be ensured even if the components are subjected to repeated cooling/heating cycles. That is, in Patent Document 1, a low elastic resin layer is disposed under the metal foil in order to reduce the stress applied to a solder connection portion.
The metal-clad laminate obtained by the method disclosed in Patent Document 1 is an approximately 1.6-mm thick composite-type copper-clad laminate in which a plurality of prepregs is superimposed. However, with a decrease in the thickness of metal foil-clad laminates in recent years, the method disclosed in Patent Document 1 was unable to sufficiently suppress a package warpage on account of a gap occurring when mold-sealing the semiconductor package with a sealing material after mounting semiconductors on a semiconductor package that uses a thin metal-clad laminate as a substrate.
Patent Document 1: Japanese Patent Application Publication No. H8-244165